The device is an extension of its controversial Active Denial System, which uses microwaves to heat the surface of the skin, creating a painful sensation without burning that strongly motivates the target to flee. The ADS was unveiled in 2001, but it has not been deployed owing to legal issues and safety fears.

Nevertheless, the Pentagon’s Joint Non-Lethal Weapons Directorate (JNLWD) in Quantico, Virginia, has now called for it to be upgraded. The US air force, whose radar technology the ADS is based on, is increasing its annual funding of the system from $2 million to $10 million.

The transmitting antenna on the current system is 2 metres across, produces a single beam of similar width and is steered mechanically, making it cumbersome. At the heart of the new weapon will be a compact airborne antenna, which will be steered electronically and be capable of generating multiple beams, each of which can be aimed while on the move.

The ADS has been dogged by controversy. Jürgen Altmann, a physicist at Dortmund University in Germany, showed that the microwave beams can cause serious burns at levels not far above those required to repel people. This was verified when a US airman was hospitalised with second-degree burns during testing in April 2007.

The airborne version will not make it any less contentious. “Independent of the mode of production, with this size of antenna the beam will show variations of intensity with distance – not just a simple decrease – up to about 500 metres,” says Altmann. Shooting it on the move with any accuracy will be difficult, he adds.

Dave Law, head of the technology division of the JNLWD, says the new antenna will operate at the lowest possible effective power level and will have a sophisticated automated target-tracking system.

In a recent cost-benefit analysis, the US Government Accountability Office rated the ADS worst out of eight non-lethal weapons currently in development.

If you think drone aircraft are all the rage at the U.S. Air Force, just wait a few years. The men in the Pentagon who look into the future believe UAVs — Unmanned Aerial Vehicles, or pilotless planes — are the future.

Comparing today’s drones to the development of manned military flight, “we are in the 1920s,” said Lt. Gen. David Deptula. He spoke at a Defense Department briefing looking 30 years into the future.

UAV’s are already used, principally for reconnaissance, where they can fly high and steady. But Defense Department planners say they can foresee drones used as cargo planes, bombers or fighters.

Planners also say they imagine the development of nano-aircraft the size of bugs, which could be used to spy inside enemy buildings.

They expect to see jets that could fly at hypersonic speeds, far beyond the ability of even the hottest pilot to keep them under control.

And they painted a picture of multi-purpose unmanned planes, which could be fitted with “pods” up front for specific missions.

A drone can be remote-controlled, steered by a “pilot” on the ground at a U.S. base, far from danger. Or, eventually, they could be self-controlled, following a preset flight plan but changing it as conditions change during its mission. The Air Force says it has seen a more than 600 percent increase in demand for unmanned missions in the past decade.

“They are very important and very effective,” in targeting enemies, said Deptula. He said drones hit what they are aiming at 95 percent of the time.

30-Year ‘Flight Plan’

In the Pentagon’s Unmanned Aircraft Systems Flight Plan, which looks out to the year 2047, the sky is basically the limit, say the planners. They said they made their ideas public in order to attract interest from aerospace companies and university engineers, who are likely to come up with leading-edge innovations — but need to know what the Air Force, the CIA and other users think they will need in the future.

The plan also suggests what the Air Force calls a loyal wingman concept. In this scenario, a pilot in a conventional manned aircraft could fly to a target, followed by a dozen or more heavily armed drones. The pilot, after dropping the bombs or missiles on his own plane, could then assign his “loyal wingmen” to do the same. It would be highly efficient — an entire squadron, led by one pilot.

Future Flight: Hypersonic Fighter Jets, No Pilots

The Air Force is also experimenting to see how many drones one operator, back at a base, can control remotely at once. With a sufficiently advanced autopilot, a drone is unlikely to need full-time piloting.

There are obstacles to overcome. Right now drones are operating in airspace controlled by the U.S. or its allies — but they are far from being ready to tangle with enemy pilots. If they are flying in contested airspace, “they’ll start falling like rain,” said Gen. Deptula. So the Air Force will consider stealth and other technologies to protect the drones in hostile territory.

Deptula couldn’t suggest a ratio of manned to unmanned aircraft in the years to come, but he said it’s clear UAV’s are a big part of the future. As the No. 2 man in the Air Force, Gen. William Fraser, said, “We have embraced this technology.”